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Mr. Kevin T. HaroffAft Page $ overstate the amount of small-sized particles present in the sample." In its March 3, 1990 analytical report, RJ Lee stated that "the fine particulate (< ten Am) in the surge bin appears to be shards and broken pieces." In addition, while manipulating particles with tweezers for observation under scanning electron microscope, AIHL noted that the larger particles were brittle and that "these fragments disintegrated easily whenever picked up by the tweezers. " None of these techniques subjected the ash to extremes which would be abnormal to find in actual handling practices. It is, therefore, reasonable to assume that the particles could be fractured during routine handling into particles less than or equal to ten µm (or even five µm) in size, and, from RJ Lee's observations, it is seen that fracturing does occur. It is obvious from analysis of the data provided for this ash that there are severe limitations on the amount of confidence which can be placed in the data representing concentrations of particle constituents of the ash. Both sampling techniques and analytical methods for measuring quantities, types, and sizes of silica particles produce results which may be subjective. These analytical methods can underestimate the concentrations of small sized particles in the ash due to agglomeration of small sized particles in the bulk samples and adherence of particles to sifting equipment. Sampling techniques can "lose" smaller particles due to air dispersal. These limitations are also evidenced by the wide fluctuations of reported free crystalline silica content of the ash, ranging from below 0.3 to 62.4 percent. These fluctuations did not correlate with incineration temperature or any specific operating parameter, and appeared random. The Wadham Energy Company has evidently acknowledged that its ash poses a hazard in its letter of June 16, 1989 warning of the dangers associated with silica exposure and urging that everyone coming into contact with the ash be properly protected. Wadham's MEDS indicates that the rice hull ash presents an inhalation hazard. It further identifies silicosis as the chronic effect of exposure, and recommends respiratory protection. The primary concern regarding the silica present in Wadham's ash is the hazard posed by inhalation of the particles. It is difficult to make a correlation between the concentration of respirable silica particles in the ash to known airborne particulate thresholds which have been accepted as "safe" or as "no adverse effect levels." CalOSHA has established an occupational "permissible exposure limit" (PFL) of 0.05 mg/m for free crystalline silica, and 0.10 mg/m for amorphous silica. These thresholds are based on time weighted averages of exposure.